A power transmission path for a wheel loader engine is provided with a transmission having a forward clutch and a reverse clutch.
When a forward/reverse switch lever arranged in a driver seat is operated to the forward position while the vehicle is traveling in reverse, for example, a gear shift command is generated to select the forward clutch. Thereby, the transmission is switched from the reverse clutch used before gear shifting to the selected forward clutch to be used after gear shifting, and the engine power is transmitted to the selected forward clutch of the transmission to be used after the gear shifting to drive the drive wheels. Thus, the vehicle is switched over from reverse travel to forward travel.
Wheel loaders are often operated in V-shape driving mode to perform works. The “V-shape driving mode” refers to a driving mode in which a wheel loader is operated to repeatedly travel back and forth along a route, firstly traveling forward to the ground to excavate soil, then traveling in reverse after the excavation until reaching a point to change the direction, and again traveling forward to load the excavated soil on a hopper or a dump truck.
During the operation in the V-shape driving mode, switching from reverse travel to forward travel, or vice versa is performed in a complicated manner.
Switching from reverse travel to forward travel, for example, is carried out, as shown in FIG. 6(a), by reducing the clutch pressure Pt of the reverse clutch from a set pressure P1, and subsequently increasing the clutch pressure Pt of the forward clutch to the set pressure P1.
An input clutch (modulation clutch) is provided between the engine and the transmission on the power transmission path of the wheel loader engine.
This input clutch is provided for adjusting the power transmitted to the traveling power train to increase the power transmitted to the work machine according to the work situation, or to prevent slippage of the vehicle.
Patent Publication 1 specified below describes an invention according to which the degree of engagement of the input clutch is controlled to prevent slippage of the vehicle.
Patent Publication 1: Japanese Patent Application Laid-Open No. 2001-146928